Projection type display apparatus

ABSTRACT

An analyzing-synthesizing optical system has the structure in which for each of the three primary colors of R, G, and B, there are provided a light valve for modulating incident light and a polarization beam splitter for guiding specific polarized light to this light valve and extracting only modulated light coming from the light valve to output it, wherein these light valves and polarization beam splitters are fixed as integrated with a synthesizing optical system comprising a cross dichroic prism and wherein optical path lengths of optical paths of the respective colors are adjusted to be almost equal to each other. A projection image display apparatus comprises the analyzing-synthesizing optical unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection type display apparatususing a plurality of light valves and, more particularly, to aconstituent part mainly including a synthesizing optical system forsynthesizing beams projected from respective light valves in theprojection type display apparatus.

2. Related Background Art

Such projection type display apparatus as a color projector are used aslarge-screen image display apparatus and the projection type displayapparatus of this type are classified under a method called a singleplate method for directly magnifying and projecting a color image and amethod called a three plate method for synthesizing images of the threeprimary colors R (red), G (green), B (blue) and projecting thesynthesized image. The three plate method requires more complexapparatus structure than the single plate method, but is easier in coloradjustment and more advantageous in color reproduction, resolution, andso on than the single plate type. The three plate method is thuspopularly employed in imagery equipment or the like.

An example of such three plate method projection type display apparatusis shown in FIG. 18. White source light including the respective colorsR, G, B, emitted from a light source not illustrated, is split into twodirections of respective polarization components by polarization beamsplitter 11'. Only R light in the component reflected by thepolarization beam splitter 11' is transmitted by red transmittingdichroic filter 52 to enter light valve 12R for R signal. The R light ismodulated to light having an image signal of R signal and this lighttravels again through the red transmitting dichroic filter 52 to enterthe polarization beam splitter 11'. Only the signal component isextracted from the light in the polarization beam splitter 11' to beoutputted. On the other hand, the G light component of the polarizedlight component transmitted by the polarization beam splitter 11' isreflected to branch off by green reflecting dichroic mirror 51 to enterlight valve 12G for G signal. The G light is modulated to light havingan image signal of G signal to be reflected. Then the light is againreflected by the green reflecting dichroic mirror 51 to enter thepolarization beam splitter 11', in which only the signal component isextracted to be outputted. The B light component in the lighttransmitted by the green reflecting dichroic mirror 51 is extracted byblue transmitting dichroic filter 53 to enter the light valve for Bsignal. The B light is modulated to light having an image signal of Bsignal to be reflected. Then the light travels again through the bluetransmitting dichroic filter 53 and then through the green reflectingdichroic mirror 51 to enter the polarization beam splitter 11', in whichonly the signal component is extracted to be outputted. As a result, thesignal components R, G, B are synthesized by the polarization beamsplitter 11' and the synthetic light is outputted to be enlarged andprojected through projection lens 14 onto a screen not illustrated.Unwanted light components are outputted along the direction of thesource light, so that they are not mixed in the synthetic light.

The components of the optical system including these reflection typelight valves and polarization beam splitter were mounted individually ona mounting base, e.g. on a mounting base forming a floor member of ahousing of the apparatus, thereby achieving the desired placement amongthe components. In other words, this conventional projection typedisplay apparatus had the structure in which the components were fixedto each other through the mounting base and in which the positionalrelation among the components was determined through the mounting base.Materials for this mounting base were aluminum alloys, fiber reinforcedresins, and so on, which were light in weight and had high workability.

SUMMARY OF THE INVENTION

This structure, however, had the problem of occurrence of so-calledregistration deviation that the base experienced elongation ordistortion with change in the ambient temperature during operation tocause deviation of positional relation among the optical members, so asto alter positions of respective color pixels relative to each other onthe screen. Particularly, in the case of the recent projection typedisplay apparatus for projection onto a large screen, the registrationdeviation heavily degraded the projected image, which was a seriousproblem.

The present invention has been accomplished under the above-describedcircumstances and an object of the present invention is to provide anoptical system for projection type display apparatus that can reduce theregistration deviation, thereby improving the quality of projectedimage.

The inventors contemplated that the above registration deviationoccurred as follows; the floor member on which the above-stated lightvalves, analyzing optical system, and color synthesizing optical systemwere fixedly mounted experienced expansion and contraction with changein the ambient temperature to change the positions of the componentsmounted thereon, so that the pixels of the respective colors deviatedfrom their original positions achieved by initial positioning.

First of all, in order to decrease the expansion and contraction of thefloor member due to the temperature change, a conceivable way is toselect a material having a small thermal expansion coefficient for thefloor member. In general, iron-based materials as a typical example ofsuch material have a drawback of large weight and thus are not usedeasily. Further, nickel alloys typified by invar with small thermalexpansion coefficient reveal poor workability and are very expensive.

The inventors considered that the above problem could be solved whileusing the conventional aluminum alloys or fiber reinforced resins as thematerial for the floor member, and accomplished the present invention.

As a result, the inventors found that the aforementioned registrationdeviation was reduced by integrally forming the optical system throughwhich the modulated light beams emitted from the respective light valvestraveled to be color-synthesized and outputted and that, further byfixing a member closest to the projection lens out of the thusintegrated members to the floor member, focus deviation of projectedimage was also reduced in combination with the integration effect. Thisis because the change in distance with temperature change becomesignorable when the distance is small between the fixed member and theprojection lens fixed to the floor member.

The present invention provides an analyzing-synthesizing optical systemunit for projection image display apparatus in which beams of the threeprimary colors of R, G, and B are modulated by respective, dedicatedpolarization beam splitters and light valves, the modulated beams areextracted, and a synthesizing optical system synthesizes the three colorbeams to output synthetic light, wherein the light valves and thepolarization beam splitters are fixed as integrated with thesynthesizing optical system and wherein optical path lengths of opticalpaths for the respective colors, established by each light valve, eachpolarization beam splitter, and the synthesizing optical system, areapproximately equal to each other.

In this structure, the members constituting each optical path areintegrated without intervention of the mounting base, so that thepositional relation among the components is independent of the mountingbase. With change in the ambient temperature, the relative positionaldeviation between the light valves will result from only deviationcaused by dimensional change of the members including the light valves,polarization beam splitters, and so on, and is completely free of theexpansion and contraction of the mounting base accordingly. Therefore,amounts of the deviation can be reduced remarkably when compared withthe deviation due to the thermal expansion coefficient of the projectiontype display apparatus as in the conventional projection type displayapparatus described above. Further, amounts of the deviation caused bythe dimensional change of the members are almost equal because of theapproximately equal path lengths, so that the effect thereof is furtherrelaxed. Therefore, even if the material for the mounting base isselected from the aluminum alloys and the fiber reinforced resins withrelatively large thermal expansion coefficients in view of the weightreduction, workability, and cost, the registration deviation can bereduced largely and the quality of projected image can be improved, ascompared with the conventional projection type display apparatus.

The present invention also offers an optical system unit for projectionimage display apparatus in which incident white light is polarized andseparated by a polarization beam splitter to be separated into beams ofthe three primary colors of R, G, and B by a separating-synthesizingoptical system, the beams are modulated by respective, dedicated lightvalves, the modulated beams are synthesized again by the aforementionedseparating-synthesizing optical system, and only the modulated light isextracted by the above polarization beam splitter, wherein the lightvalves and the polarization beam splitter are fixed as integrated withthe synthesizing optical system and wherein optical path lengths ofoptical paths of the respective colors, established by each light valveand the separating-synthesizing optical system, are approximately equalto each other.

In this case, the separating optical system is also integrated, which isfurther preferable. This also has the effect of making the entireoptical system compact.

When these optical systems are applied to the projection type displayapparatus, the projection type display apparatus can be achieved withless registration deviation and less focus deviation. The presentinvention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram to show an optical pathconfiguration of the first embodiment of the present invention;

FIG. 2 is a perspective view of the configuration of the firstembodiment;

FIG. 3 is a perspective view to show the relation among a cross dichroicprism, three polarization beam splitters, and a member used forintegrating them in the first embodiment;

FIG. 4 is a perspective view to show a joint state between the lightvalves and the polarization beam splitters in the first embodiment;

FIG. 5 is an overall schematic diagram to show an optical pathconfiguration of the second embodiment of the present invention;

FIG. 6 is a perspective view of the configuration of the secondembodiment;

FIG. 7 is a perspective view to show the structure of a modification ofthe second embodiment;

FIG. 8 is a perspective view to show the structure of anothermodification of the second embodiment;

FIG. 9 is a perspective view to show still another modification of thesecond embodiment;

FIG. 10 is a perspective view to show the structure of the thirdembodiment of the present invention;

FIG. 11 is an overall schematic diagram to show an optical pathconfiguration of the fourth embodiment of the present invention;

FIG. 12 is a perspective view of the configuration of the fourthembodiment;

FIG. 13 is an overall schematic diagram to show an optical pathconfiguration of the fifth embodiment of the present invention;

FIG. 14 is a perspective view of the configuration of the fifthembodiment;

FIG. 15 is a detailed perspective view to show the structure of a prismportion in the fifth embodiment;

FIG. 16 is an overall schematic diagram to show an optical pathconfiguration of the sixth embodiment of the present invention;

FIG. 17 is a perspective view of the configuration of the sixthembodiment; and

FIG. 18 is an overall schematic diagram of the conventional projectiontype display apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several preferred embodiments of the present invention will be describedin detail by reference to the accompanying drawings. To facilitate thecomprehension of the explanation, the same components will be denoted bythe same reference numerals in the drawings as much as possible, andredundant description will be omitted.

[First Embodiment]

FIG. 1 is a schematic diagram to show the overall structure of the firstembodiment according to the present invention.

This projection type display apparatus is mainly composed of atrichromatic separation optical system for separating the source lightinto beams of the three primary colors R, G, and B and ananalyzing-synthesizing optical system for producing projected images ofthe respective colors and synthesizing them. Among them, thetrichromatic separation optical system is composed of a mirror 3 forguiding the source light, a cross dichroic mirror 4 for separating the Blight from the mixed light of G light and R light, disposed on the exitoptic axis of the mirror 3, a mirror 8 for guiding this B light to theanalyzing-synthesizing optical system, disposed on the optic axis of theB light after the separation, a mirror 7 for changing a travelingdirection of light, disposed on the optic axis of the mixed light of Glight and R light after the separation, and a dichroic mirror 9 havingsuch characteristics as to reflect the G light and transmit the R light.This cross dichroic mirror 4 is constructed in the X-configurationconsisting of a dichroic mirror 5 having such characteristics as toreflect the B light and transmit the G light and R light and a dichroicmirror 6 having such characteristics as to reflect the G light and Rlight and transmit the B light, intersecting with each other.

The analyzing-synthesizing optical system 20, as shown in theperspective view thereof in FIG. 2, is constructed by integrating lightvalves 112R, 112G, 112B for the respective color beams, polarizationbeam splitters (PBSs) 11R, 11G, 11B, and a cross dichroic prism 13 forsynthesis. For convenience' sake of description, the mutually orthogonalcoordinate axes X, Y, and Z are defined as illustrated (which are alsoused in each of the drawings which follow).

The cross dichroic prism 13 has such structure that four rectangularequilateral triangle prisms having a common refractive index, which haveR light reflecting dichroic film 13R or B light reflecting dichroic film13B of a dielectric multilayer film on their predetermined slant faces,are combined with each other with their right-angle parts being joinedand that they are bonded with an adhesive in a perpendicularly crossingpattern of X-shape of the R light reflecting dichroic film 13R and Blight reflecting dichroic film 13B.

The PBSs 11R, 11G, 11B have the structure in which a polarizationseparating film made of a dichroic multilayer film designed and formedfor each color light is deposited by physical vapor deposition such asvacuum vapor deposition on a bottom surface of one of two optical glassprisms having the cross-sectional shape of a rectangular equilateraltriangle and a common index of refraction and in which the film surfaceis bonded to a bottom surface of the other prism with an adhesive. Theyare secured by holding member 31 in such arrangement that the PBS 11Rfor R color and the PBS 11B for B color are opposed to each other oneither side of this cross dichroic prism 13 and that the PBS 11G for Gcolor is located perpendicular thereto. In this case, each polarizationseparating film of the PBS 11R, 11G, or 11B is located so as to reflectone polarization component of the R light, G light, or B light and makeit travel in the Y-direction, in the X-direction, or in the-Y-didirection, respectively, i.e., away from the cross dichroic prism13.

Further, each light valve 112R, 112G, 112B is attached through mountingmember 21R, 21G, 21B and mount member 22R, 22G, 22B to the PBS for eachcolor 11R, 11G, 11B. The surface of the cross dichroic prism 13 oppositeto the surface facing the PBS 11G is an exit plane of synthetic light.The projection lens 14 is located on the optic axis of the syntheticlight as shown in FIG. 1.

FIG. 3 shows the structure of the holding member 31. The holding member31 is formed basically in a rectangular solid shape and has a space forhousing the dichroic prism 13 for synthesis of color inside thereof.This holding member 31 is molded by diecasting of aluminum and istreated by a surface blacking treatment such as a black alumitetreatment for keeping the predetermined shape and for preventingscattering of incident light. The holding member 31 has an aperture 32as an entrance through which the dichroic prism 13 for synthesis ofcolor is set into this space, in the top surface (in the Z-direction).Namely, the dichroic prism 13 is guided through the aperture 32 fromabove to inside the holding member 31 as shown in FIG. 3 and the fourcorner ridges of the dichroic prism 13 are fixed to portions of theholding member 31 facing thereto with an adhesive.

Further, this holding member 31 is constructed in the structure havingapertures 33R, 33B, 33G, 34 in the Y-direction, the -Y-didirection, theX-direction, and the -X-direction as well, and these apertures are opento the above-stated space for housing the cross dichroic prism 13. Amongthese apertures, the X-directional, Y-directional, and -Y-didirectionalapertures 33G, 33R, 33B are provided for guiding the modulated lightfrom each color light valve 112G, 112R, 112B (see FIG. 1 and FIG. 2),transmitted by each color light PBS 11G, 11R, 11B, to the cross dichroicprism 13. Each of members 35R, 35B, 35G forming an external frame ofthese apertures 33R, 33B, 33G functions as a stopper for positioningeach color PBS 11R, 11G, 11B so as to prevent positional deviationthereof in the -Y-didirection, in the -X-direction, or in theY-direction, respectively. Further, the holding member body 31 isprovided with holding portions 36R, 36B, 36G projecting in theY-direction, in the -Y-didirection, and in the X-direction,respectively, so as to locate and fix each PBS 11R, 11G, 11B at theposition where each PBS is positioned. A tip portion of each PBS 11R,11G, 11B is put into each holding portion 36R, 36B, 36G to be bonded andfixed, thereby being integrated therewith.

FIG. 4 is a drawing to show a process for attaching the light valves112R, 112B, 112G for the respective colors to the member incorporatingthe dichroic prism 13 and the PBSs 11R, 11B, 11G for the respectivecolors as described above. The first mounting member 22R, 22G, 22B andthe second mounting member 21R, 21G, 21B are used for attaching eachlight valve 112R, 112G, 112B to the corresponding PBS 11R, 11G, 11B asdescribed previously. The following description will be given mainlywith an example using the R color PBS 11R, light valve 112R, firstmounting member 22R, and second mounting member 21R. The structure forthe G color and for the B color is also essentially the same.

The first mounting member 22R is a member made by press working of ironsheet (SPC material), and the entire surface of the member is plated bytin-lead plating. The first mounting member 22R is formed in the shapehaving an aperture 22RA a little larger than an image forming portion ofthe light valve 112R, in the almost center portion thereof and havingfour legs 22R-1, 22R-2, 22R-3, 22R-4 on the side faces, the four legsbeing soldered to the second mounting member 21R as described below andprojecting two in the X-direction and two in the -X-direction. Further,the first mounting member 22R has portions 22R-5, 22R-6 bent andprojecting each in the -Y-didirection at the top (Z-directional) andbottom (-Z-directional) edges of the member 22R and in a predeterminedwidth in the X-direction. The first mounting member 22R is mounted onthe PBS 11R in the sandwich structure in which the R-light entranceplane of the R light PBS is interposed between these portions 22R-5,22R-6. The first mounting member 22R is fixed to the PBS 11R in thatstate with an adhesive. Described herein was the method for attachingthe mounting member 22R after the PBS 11R has been mounted on theholding member 31, but the PBS 11R may be fixed to the holding member 31after the mounting member 22R has been mounted on the PBS 11R priorthereto.

Next described is the second mounting member 21R. This member 21R ismade by punching of the same SPC material as the first mounting member22R and plating the entire surface by tin-lead plating. The shape of thesecond mounting member is identical to that of the first mounting memberin that it has an aperture in the near center and legs 21R-1, 21R-2,21R-3, 21R-4 on the both sides, but the second mounting member 21R isflat as a whole with no bent portion corresponding to 22R-5, 22R-6 ofthe first mounting member. The second mounting member 21R is providedwith three threaded holes for mounting of the light valve 112R. Thesecond mounting member 21R and light valve 112R need to be preliminarilyfixed by screwing by use of the threaded holes and screws.

Now, let us briefly explain the light valve 112R used in the presentembodiment.

The light valve 112R is composed of a liquid crystal light valve body12R and a holding member made of a resin for protecting it, so that theliquid crystal light valve body 12R is protected by the resin memberexcept for its entrance/exit plane. When the light valve 112R isobserved from the back, the resin protecting portion appears as shown inFIG. 4; when observed from the front, the entrance/exit plane of thelight valve body 12B appears through the aperture as in the light valve112B shown in FIG. 4. The light valve 112R has holes on the entranceside thereof, for screwing the light valve 112R to the second mountingmember 21R.

This light valve body 12R is a reflection type liquid crystal lightvalve, which is of a type called an electrically addressed reflectiontype liquid crystal light valve among such reflection type light valves.

The structure of the body, which is not illustrated, consists of, fromthe entrance plane, a glass substrate, a transparent electrode (ITO;indium tin oxide), a liquid crystal modulation layer, metal electrodesforming the pixels, nonlinear switching elements such as TFTs (thin filmtransistor), and an Si substrate. When a predetermined voltage is placedbetween a metal electrode and the transparent electrode by switching ofTFT, liquid crystal molecules in the liquid crystal layer change theiralignment, so as to function as a modulation layer. This function isutilized. Specifically, when the voltage is applied to the liquidcrystal layer by the switching, the liquid crystal molecules in theliquid crystal layer are aligned along the electric field so as tofunction as a quarter wave plate layer. Because of this function,linearly polarized light entering the pertinent portion is converted tocircularly polarized light after passage through the liquid crystallayer. The circularly polarized light is reflected by the aforementionedmetal reflecting electrode and again travels through the liquid crystallayer. Then the light emerges from the light valve in the form oflinearly polarized light whose oscillation direction is shifted 90° fromthat of the incident linearly polarized light. When the incident lightis s-polarized light (or p-polarized light), the outgoing light isp-polarized light (or s-polarized light). On the other hand, the liquidcrystal molecules in the liquid crystal layer are not aligned inportions to which the aforementioned voltage is not applied, but theyare oriented following the liquid crystal orientation layer to composethe twisted structure in the thickwise direction of the layer.Therefore, the linearly polarized light incident into such portionstravels as being rotated along the twisted structure, and the light isreflected by the metal reflecting electrode. Then the light travels inthe opposite direction as also being rotated along the twistedstructure, and the light is emergent from the light valve in the form ofthe same linearly polarized light as upon incidence into the lightvalve. When the incident light is s-polarized light (or p-polarizedlight), the outgoing light is also s-polarized light (or p-polarizedlight). The above described the structure of the electrically addressedreflection type light valve and the function thereof.

This light valve body 12R is not limited to the electrically addressedreflection type light valve, but an optically addressed reflection typelight valve may also be adopted.

When the second mounting member 21R with this light valve 112R mountedthereon is fixed to the first mounting member 22R, it is necessary toachieve adjustment with the other light valves 112G, 112B, i.e., toachieve registration among the colors on the light valve bodies 12R,12B, 12G and conjugateness of each light valve with respect to theprojection lens (i.e., the positions of focus should be equal among thelight valves). Therefore, each light valve 112R, 112G, 112B is mountedthrough the second mounting member 21R, 21G, 21B onto the first mountingmember while keeping it in an image projecting state.

First, the legs 22G-1 to 22G-4 of the first mounting member 22G arematched with the corresponding legs 21G-1 to 21G-4 of the secondmounting member 21G and then the solder on the border is locally heatedto solder them with each other, thereby fixing them.

Although the legs of the two members were preliminarily solder-plated,this soldering work will become easier if prior to execution of thiswork an additional amount of solder is placed on the opposing surfacesof one or both of the first mounting member and the second mountingmember.

The local heating can be achieved by temporarily securing the legs ofthe first mounting member and the second mounting member in an opposingstate and irradiating the legs with laser to sweat the solder. Afterthat, the sweat solder becomes adhering to the solder preliminarilydeposited by tin-lead plating and soldering is achieved by cooling it.

Since this work is carried out between the legs of the projectingstructure on the both sides of the first holding member and secondholding member, they can be soldered at the portions apart from thelight valve and PBS, whereby this structure can minimize the effect ofincrease in temperature due to the soldering.

Since the light valve body itself does not have high heat resistance atall, the soldering by this structure is very effective.

Next, the first mounting member 22R and second mounting member 21R arecoupled by soldering. On this occasion, the soldering is carried outwhile adjusting the position of soldering and the thickness of solder soas to achieve coincidence of registration between the pixels of the Glight and R light over the entire surface and achieve the focus at thesame position.

Further, the first mounting member 22B and second mounting member 21Bare coupled by soldering so as to achieve coincidence of registration ofthe pixels of B light with their corresponding pixels of R light and Glight, having already been aligned with each other.

The above achieves registration of the light valves 112R, 112B, 112G andconjugateness with respect to the projection lens.

This work may be one conducted after mounting of the projection lens ofthe projection apparatus, but the projection apparatus may be assembledin such a way that a dedicated jig is produced, the integrated,analyzing-synthesizing optical system 20 of the present embodiment shownin FIG. 2 is constructed thereby, and the projection apparatus isassembled using the integrated optical system.

The analyzing-synthesizing optical system 20 shown in FIG. 2, producedas described above, is fixed by attaching only the holding member 31 tothe floor part of the housing of the projection apparatus. This fixingmay be effected by bonding or by preliminarily making threaded portionsat the four corners of the bottom portion of this holding member 31 andscrewing it to the floor portion through the threaded portions. Thislocates the analyzing-synthesizing optical system 20 relative to thetrichromatic separation optical system and projection lens 14 as shownin FIG. 1.

Next, the operation of this apparatus will be described referring toFIG. 1. The source light emitted from the light source not illustratedturns its traveling direction at the mirror 3 to enter the crossdichroic mirror 4 and to be split into the B light and the mixed lightof R and G light. Among the split beams, the mixed light of R light andG light is guided to the dichroic mirror 9 by the mirror 7 to be splitinto the G light and the R light. This G light or R light is incident tothe PBS 11G or 11R, respectively. On the other hand, the B light splitby the cross dichroic mirror 4 is made incident to the PBS 11B by themirror 8.

The polarization separating portion of each PBS 11R, 11G, 11B separatesthe light into polarization components by reflecting light of only onespecific polarization component and transmitting light of the otherpolarization component. Only the polarization component reflected ismade incident to the light valve 112B, 112G, 112R placed for each colorlight. The reflected light emerging from the light valve, includinglight modulated by a signal of each color light, is again incident toeach PBS 11R, 11G, 11B. The polarization separating portion of PBStransmits the polarization component different from the reflectedpolarization component, i.e., transmits only the modulated light oranalyzes the light to output only the modulated light. These beams areincident through the different entrance surfaces for the respectivecolors into the cross dichroic prism 13 forming the color synthesizingoptical system. The B light reflecting dichroic film 13B and the R lightreflecting dichroic film 13R placed in the X-shape in the cross dichroicprism 13 reflect the B light and the R light, respectively, and transmitthe G light, thus achieving synthesis of the three colors. The thussynthetic light is emitted from the prism and the projection lens 14enlarges the image to project the enlarged, full color image onto thescreen not illustrated.

In the conventional projection apparatus, the analyzing-synthesizingoptical system was not axially symmetric with respect to the optic axisand the components were fixed individually to the floor member;therefore, this structure gave rise to deviation in the normal directionto the optic axis of the light valve with change in temperature, so asto result in deviation of registration. When the analyzing-synthesizingoptical system described in the present embodiment is applied to theprojection type display apparatus, the light valves, PBSs, and dichroicprism are axially symmetric with respect to the optic axis and theaxially symmetric structure is maintained even with change intemperature, however; therefore, the light valves will shift along thedirection of the optic axis, but will never shift in the normaldirection to the optic axis. Hence amounts of the deviation can bereduced largely as compared with the conventional structure, so that theregistration deviation can be reduced.

When environment resistance of the projection type display apparatus istaken into account, to use a glass material having a small photoelasticconstant (the photoelastic constant not more than 1.5×108 cm² /N) as aglass material for the three PBSs of the analyzing-synthesizing opticalsystem unit described above is very effective in order to obtain a goodprojected image, because such glass material reveals less occurrence ofbirefringence caused by change in the ambient temperature, stressappearing during mounting, or the like and is thus free of illuminancenonuniformity, so as to enhance the contrast of projected image.

[Second Embodiment]

The basic form of the second embodiment of the present invention will bedescribed next referring to FIG. 5 and FIG. 6.

FIG. 5 is a schematic, structural drawing to show the projection typedisplay apparatus of the present embodiment. FIG. 6 is a schematic,perspective view to show the analyzing-synthesizing optical system 20 inthe projection type display apparatus shown in FIG. 5.

The fundamental structure of this projection type display apparatus isthe same as in the first embodiment shown in FIG. 1. The secondembodiment is different from the first embodiment in that the lightvalves 12R, 12B, 12G are fixed directly to the respective PBSs 11R, 11G,11B with an adhesive and in that the PBSs 11R, 11G, 11B and the crossdichroic prism 13 are coupled without using the constituent member 31but they are fixed through path length correcting member 15R, 15G, 15Bwith an adhesive.

These path length correcting members 15R, 15G, 15B are optical glassmembers of a rectangular solid shape having a predetermined thickness.

In the present embodiment, as shown in FIG. 5 and FIG. 6 (particularly,in FIG. 5), the analyzing-synthesizing optical block 20 is made byintegrating the PBSs 11R, 11G, 22B, the light valves 12R, 12G, 12B, thecross dichroic prism 13, and the path length correcting members 15R,15G, 15B without intervention of the mounting base (not illustrated).Namely, these elements 11R, 11G, 11B, 12R, 12G, 12B, 13, 15 are bondedwith an adhesive to be integrated in the present embodiment.Specifically, the path length correcting member 15R, 15G, 15B is bondedto the entrance surface for each color light of the cross dichroic prism13 with an adhesive and a predetermined surface of each color light PBS11R, 11G, 11B is bonded to the surface opposite to the bond surface ofthe corresponding path length correcting member 15R, 15G, 15B. Further,the entrance surface of each light valve 12R, 12G, 12B is bonded to thesurface opposite to the bond surface of each PBS 11R, 11G, 11B with anadhesive.

The thicknesses of these path length correcting members 15R, 15G, 15Bare adjusted as follows; the dimensions of the PBSs 11R, 11G, 11B andthe cross dichroic prism 13 are preliminarily measured and the opticalpath lengths are made nearly equal to each other from the bond surfaceof each PBS 11R, 11G, 11B bonded to the light valve 12R, 12G, 12B up tothe exit plane of the cross dichroic prism 13.

Although not illustrated in the drawings, the analyzing-synthesizingoptical block 20 is mounted as fixed to the mounting base, for exampleto such a mounting base as the floor member forming the housing of theapparatus of the present embodiment. This means that the elements 11R,11G, 11B, 12R, 12G, 12B, 15 except for the cross dichroic prism 13 ofthe analyzing-synthesizing optical block 20 are fixed through the crossdichroic prism 13 to the mounting base. This fixing can be made, forexample, by bonding only the bottom surface of the cross dichroic prism13 to the mounting base with an adhesive or the like or by attachingonly the bottom part of the cross dichroic prism 13 to the mounting basewith a mounting bracket.

As a matter of fact, the analyzing-synthesizing optical block 20 may befixed to the mounting base by fixing only either one of the elements11R, 11G, 11B, 12R, 12G, 12B, 15 except for the cross dichroic prism 13.It is more preferable, however, to employ the fixing way of the presentembodiment in which the cross dichroic prism 13 is fixed directly to themounting base and in which the other components 11R, 11G, 11B, 12R, 12G,12B, 15 are fixed through the cross dichroic prism to the mounting base,because this structure can decrease the focus deviation of projectedimage.

This is from the following reason; since the projection lens 14 is fixedto the mounting base separately from the analyzing-synthesizing opticalblock 20, the positional relation between the projection lens 14 and theanalyzing-synthesizing optical block 20 is determined through themounting base. Consequently, the positional relation between theprojection lens 14 and the analyzing-synthesizing optical block 20varies depending upon expansion or contraction of the mounting base withchange in the ambient temperature, and the focus deviation of projectedimage occurs according thereto. When the cross dichroic prism 13 closestto the projection lens 14 out of the components of the integrated block20 is fixed directly to the mounting base as in the present embodiment,the distance is small between the fixing position of the projection lens14 and the fixing position of the analyzing-synthesizing optical block20 in the mounting base, however. In that case, the change is small inrelative positional relation between the projection lens 14 and theintegrated block 20 with change in the ambient temperature even in thecase of a material having a relatively large thermal expansioncoefficient being used as a material for the mounting base. As a result,the focal deviation of projected image is also decreased. Particularly,if the distance is sufficiently small between the projection lens 14 andthe cross dichroic prism 13, the focal deviation of projected image withchange in the ambient temperature will become negligible.

The present embodiment also requires the so-called registrationadjustment for aligning the corresponding pixels of the respective lightvalves 12R, 12G, 12B on the projected image, as in the first embodiment.This will be described below.

After the cross dichroic prism 13 is bonded to the path lengthcorrecting members 15R, 15G, 15B, the path length correcting member 15R,15G, 15B and PBS 11R, 11G, 11B are bonded to each other withpredetermined accuracy. Then the light valve 12G for G light isaccurately bonded to the G light PBS 11G, for example, with anultraviolet curing adhesive. In this state light is then guided so thatonly the G light is projected onto the screen; and the light valve 12Gfor G light is driven to project a projection image for adjustment (forexample, a color chart) by only the G light onto the screen.

Then the light valve 12R for R light (or the light valve 12B for Blight) is held on the R light PBS 11R without curing the ultravioletcuring adhesive and light is guided so that a projected image by the Rlight is also projected onto the screen. The projected image by the Rlight is also projected onto the screen. The light valve 12R is moved bya small amount so as to achieve registration of the pixels for R lightwith respect to the pixels for the G light, and it is then fixed. Whilekeeping this state, the adhesive is exposed to ultraviolet light to becured, whereby the light valve 12R is bonded to the PBS 11R.

After that, the light valve 12B for B light is also bonded to the PBS11B with the ultraviolet curing adhesive by the same procedures, thusproducing the analyzing-synthesizing optical block 20 while achievingthe registration adjustment among the R light, G light, and B light.

In the projection type display apparatus of the present embodiment, theoptical system through which the modulated beams of the respectivecolors emitted from the corresponding light valves 12R, 12G, 12B travelthrough the analyzing step, color synthesis, and emission, is integralwithout intervention of the mounting base and the positional relationamong the elements 11R, 11G, 11B, 12R, 12G, 12B, 13, 15 constitutingthis optical system is independent of the mounting base. With change inthe ambient temperature, deviation of relative positions among the lightvalves 12R, 12G, 12B is only deviation caused by dimensional change ofglasses for the light valves 12R, 12G, 12B, PBSs 11R, 11G, 11B, pathlength correcting members 15R, 15G, 15B, and cross dichroic prism 13composing the analyzing-synthesizing optical block 20 accordingly. Thedeviation is completely free of the expansion and contraction of themounting base, so that the deviation of optic axis can be reducedgreatly as compared with the conventional projection type displayapparatus. This permits the present embodiment to adopt the aluminumalloys, the fiber reinforced resins, etc. having relatively largethermal expansion coefficients while being light in weight, high inworkability, and low in cost, as the material for the mounting base;even under this condition the registration deviation can be reducedlargely and the quality of projected image can be improved.

FIG. 7 is a perspective, structural drawing to show a modification ofthe analyzing-synthesizing optical block of the second embodiment. Thismodification is different from the second embodiment described above inconnection between each light valve and PBS part. This modification ischaracterized by using the same fixing method as in the first embodimentshown in FIG. 2. A method for producing this modification is basically acombination of the production methods of the first embodiment and thesecond embodiment, and the functions and features thereof are the sameas those of the second embodiment. Therefore, the detailed descriptionis omitted herein.

FIG. 8 is a perspective view to show the structure of still anothermodification. This modification has the structure in which the lighttransmitted by the polarization separating film of PBS, out of the lightincident to each color PBS 11R, 11G, 11B, is guided to each light valve112R, 112G, 112B to be modulated, achieved by modifying the structure ofthe foregoing modification.

Specifically, the R light is incident to the PBS 11R in the-X-direction, the polarization component transmitted by the polarizationseparating portion of PBS 11R is incident to the light valve 112R, thelight modulated and reflected thereby is incident again into the PBS11R, only the modulated light is reflected (or analyzed) by thepolarization separating portion of the PBS 11R, the modulated light thentravels in the Y-direction, and the modulated light travels through thepath length adjusting member 15R into the cross dichroic prism 13.

The B light and the G light is also modulated in the same manner andonly the modulated light (analytic light) travels through the associatedpath length adjusting member 15B or 15G into the cross dichroic prism 13in the -Y-didirection or in the -X-direction, respectively.

The beams incident into the cross dichroic prisms 13 are synthesized bythe R light reflecting dichroic film 13R and the B light reflectingdichroic film 13B arranged in the X-shape in the dichroic prism 13, andthe synthesized light is emitted as projected synthetic light in the-X-direction.

In this modification the legs of the first mounting member 21R, 21G, 21Band the second mounting member 22R, 22G, 22B project on the left andright sides of the mounting members; they will not pose a problem on theoccasion of placement of these mounting members, because the path lengthadjusting member 15R, 15G, or 15B is interposed between the crossdichroic prism 13 and them.

In this modification shown in FIG. 8 the legs of the mounting membersproject in the ±X-directions and in the ±Y-directions; but these legscan be arranged to project all in the ±z-directions. When this structureis employed, the projecting portions of each first mounting member 22R,22G, or 22B for holding the PBS 11R, 11G, or 11B is between may beformed between the legs. This is effective where the members 15R, 15G,15B are thin in the direction of optical path length.

This modification requires higher mounting accuracy of each color PBSthan the embodiments and modification described above. The reason is asfollows; if the PBS has rotational variation around the Z-axis of thedrawing, deviation of optic axis will be two times larger in thismodification than that of the first embodiment and the foregoingmodification, because the analytic light is reflected in the PBS.

Still another modification of the second embodiment will be describednext referring to FIG. 9. FIG. 9 is a schematic, perspective view toshow the analyzing-synthesizing optical block 20 of this modification.

This modification is different from the second embodiment shown in FIG.6 in that a half wave plate 16R or 16B is placed between the path lengthcorrecting member 15R or 15B and the cross dichroic prism 13.

The purpose of placing these half wave plates 16R, 16B is as follows.The R light reflecting dichroic film 13R and the B light reflectingdichroic film 13B arranged in the X-shape in the cross dichroic prism 13have different reflecting characteristics depending upon the oscillatingdirection of polarization of light incident to the films 13R, 13B, andutilization efficiency of light is higher when polarized light withhigher reflectivity is made incident thereto. It also becomes possibleto broaden the wavelength region of reflected light. Each half waveplate 16R, 16B functions to change the oscillating direction ofpolarized light of the R light or the B light outgoing through thepolarization beam splitter 11R or 11G. As for the G lightcolor-synthesized with the R light and B light through the crossdichroic prism 13, the half wave plate is not placed, because thetransmission wavelength range can be utilized more widely andeffectively when the transmitted light is made incident without changingthe polarization direction with respect to the dichroic films 13R, 13B,conversely.

The analyzing-synthesizing optical block 20 in this modification canalso be produced by the same method as that of the second embodimentdescribed previously. It is, however, preferable that the half waveplates 16R, 16B be preliminarily bonded to the R light entrance surfaceand to the B light entrance surface of the cross dichroic prism 13,respectively. The fixing of the other members thereafter, and theregistration adjusting method of each light valve 12R, 12G, 12B are thesame as those described above.

This modification achieves the same advantages as the second embodimentdescribed above and, in addition, can change the polarization state ofeach color light incident to the cross dichroic prism 13 into thepolarization state in which the cross dichroic prism 13 cancolor-synthesize the color beams with highest efficiency, so that abright projected image can be obtained with high luminance.

In this case, however, the polarization direction of the R light and Blight included in the synthetic light is different from that of the Glight and, therefore, a polarizing screen cannot be used as a projectionscreen. In order to increase the efficiency of color synthesis in thecross dichroic prism 13 to some extent while using the polarizingscreen, a half wave plate is also interposed between the cross dichroicprism 13 and the PBS 11G so as to align the polarization directions ofthe all color beams incident to the cross dichroic prism 13 with eachother.

In this modification the half wave plates 16R, 16B are placed in theoptical paths of the R light and the B light, respectively, and it is amatter of course that the thicknesses of the path length correctingmembers 15R, 15G, 15B should be adjusted so as to keep the optical pathlengths of the respective optical paths almost equal to each other.

The locations of the half wave plates 16R, 16B do not always have to bethose shown in FIG. 9, but they may be placed between the path lengthadjusting member 15R, 15B and the PBS 11R, 11B.

[Third Embodiment]

FIG. 10 shows the analyzing-synthesizing optical block 20 of the thirdembodiment according to the present invention. The third embodiment usesa dichroic prism composed of three triangular prisms with dichroic filmson predetermined surfaces thereof, for example, without using the crossdichroic prism as the synthesizing optical system.

In the present embodiment, since the optic axis of the B light among thecolor beams is not parallel to the X-axis as detailed hereinafter, newX'-axis is defined as an axis parallel to the optic axis of the B lightbut not parallel to the X-axis on the X-Y plane in order to indicate theoptic axis of the B light as illustrated, for easier understanding ofdescription.

As illustrated, the dichroic prism 113 used in the present embodiment isa prism constructed by bonding three triangular prisms 113-1, 113-2,113-3 with an adhesive and has B light reflecting dichroic film 113B andG light reflecting dichroic film 113G at the illustrated positions,thereby possessing the color synthesizing function.

The other fundamental structure is basically the same as that of themodifications of the second embodiment shown in FIG. 7 and FIG. 8. Inthe present embodiment each color beam of the R light, the G light, orthe B light travels in the Z-direction to enter each color light PBS11R, 11G, 11B, and each light valve 112R, 112G, 112B is placed on asurface in the Z-direction of each PBS 11R, 11B, 11G, i.e., on the topsurface in the drawing. Because of this, the polarization separatingfilm of each PBS 11R, 11B, 11G is oriented so as to emit the analyticlight (modulated light) toward the dichroic prism 113. The trichromaticseparation optical system is not illustrated herein, but those whoskilled in the art can readily contemplate the structure necessary formaking the three separate color beams incident in the Z-direction intoeach PBS 11R, 11B, 11G.

The light valves 112R, 112G, 112B are mounted on the PBSs 11R, 11G, 11Bby use of the first mounting members 22R, 22G, 22B and the secondmounting members 21R, 21G, 21B in the same manner as in the firstembodiment. In the present embodiment the bent portions of the firstmounting members 22R, 22G, 22B for mounting thereof onto the PBSs 11R,11G, 11B are given between the legs for soldering of the members.

Each polarization separating portion of PBS 11R, 11G, 11B reflects onlythe modulated light of the output light modulated by the light valvebody in each color light valve 112R, 112G, 112B, and the modulated lighttravels through the path adjusting member 15R, 15G, 15B and each colorentrance surface of the dichroic prism 113 thereinto.

The detected light of the R light incident in the -Y-direction into theprism member 113-3 of the dichroic prism 113 travels straight to passthrough the dichroic prisms 113-2, 113-1 and to be emitted in the-Y-direction from the exit surface. The analytic light of the G light isincident in the X-direction into the prism member 113-2 and is reflectedby the dichroic film 113G to travel in the -Y-direction. Then the lighttravels through the dichroic prism 113-1 to be emitted in the-Y-direction from the exit surface. Finally, the B light incident in the-X'-direction into the prism 113-1 is totally reflected once by the exitsurface of this prism 113-1 to travel in the Y'-direction. Then thelight is reflected by the dichroic film 113B to travel in the-Y-direction and to be emitted in the same direction from the exitsurface. As described above, the synthesis of three colors is achievedby the dichroic prism 113, and the projected image is emitted in the-Y-direction from the same exit surface to be projected onto the screenby the projection lens not illustrated.

It is needless to mention that only the dichroic prism 113 needs to befixed to the floor member in the present embodiment as well.

[Fourth Embodiment]

The fourth embodiment of the present invention will be described belowreferring to FIG. 11.

FIG. 11 is a schematic, structural drawing to show the projection typedisplay apparatus of the present embodiment.

The optical block 20' of the present embodiment is characterized in thatthe cross dichroic prism 13 serves as a trichromatic separation opticalsystem and as a synthesizing optical system, different from the first tothe third embodiments described above. Another feature is that theanalyzing optical system has only one PBS ready for the all colors,without providing the PBSs for the respective colors.

The source light emitted from the light source not illustrated isincident in the -Y-direction into the PBS 17 and a specific polarizationcomponent of the light is separated and travels in the X-direction toenter the cross dichroic prism 13. The structure of this dichroic prism13 is the same as that in the first embodiment. The light is split bythe R light reflecting dichroic film 13R and the B light reflectingdichroic film 13B arranged in the X-shape in this dichroic prism 13, sothat the R light is reflected into the Y-direction, the B light into the-Y-direction, and the G light travels straight in the X-directionwithout being reflected. Then each beam is incident to the associatedlight valve 12R, 12B, 12G for each color. The light including themodulated light subject to modulation in these light valves is incidentagain into the dichroic prism 13 and then the R light reflectingdichroic film 13R and B light reflecting dichroic film 13B arranged inthe X-shape in the dichroic prism 13 reflect the R light and the B lightbut transmit the G light. The beams of the three colors all are bentinto the -X-direction to be synthesized and enter the PBS 17. Thepolarization separating film of the PBS 17 outputs only the modulatedlight in the -X-direction to project a full color image through theprojection lens 14 onto the screen not illustrated.

FIG. 12 is a perspective view to show the detailed structure of thisoptical system. The light valves 112R, 112G, 112B each held in a packageare mounted using the mounting members 21R, 21G, 21B, 22R, 22G, 22B inthe same manner as in the first embodiment. Each light valve 112R, 112G,112B may be mounted directly on the dichroic prism 13, but mountingthrough the path length adjusting member 15R, 15B, 15G is morepreferable, because they make it easier to adjust the optical pathlengths of the respective color beams nearly equal to each other andbecause they make adjustment of pixels easier without collision betweenthe mounting members illustrated. It is preferable that the path lengthadjusting member 15X be also interposed between the PBS 17 and dichroicprism 13, for adjustment of the position of incidence of the sourcelight.

The light valves may be attached directly to the respective path lengthadjusting members with an adhesive without using the mounting members,as in the second embodiment and the other embodiments.

In the present embodiment the trichromatic separation optical system andthe analyzing-synthesizing optical system all are integrated. When thisis held on the base at the portion of dichroic prism 13 or PBS 17, theeffect of thermal expansion etc. due to the temperature change can beminimized accordingly. The optical path lengths of the respective colorsafter the separation in the present embodiment are shorter than those inthe other embodiments, and the present embodiment thus has an advantagethat the apparatus structure is compact.

As described above, the optical block 20' of the present embodiment maybe held on the base at either portion of the dichroic prism 13 or thePBS 17. It is more preferably held on the PBS 17 side, because thepositional relation with the projection lens will not vary. When the PBS17 and path length adjusting member 15X can be made of a material havinga small thermal expansion coefficient and in a small thickness becauseof easiness of fixing, the focus deviation can also be reduced similarlyeven if the optical block is fixed on the dichroic prism 13 side.

[Fifth Embodiment]

FIG. 13 is an overall schematic view of the fifth embodiment of thepresent invention. This embodiment is characterized in that so-calledPhilips prism 213 is used instead of the dichroic prism 13 of the fourthembodiment shown in FIG. 11. FIG. 14 is a perspective view to show thestructure of the optical block 20' of this embodiment and FIG. 15 is anexploded perspective view to show the structure of part of the Philipsprism 213.

The fundamental structure of the present embodiment is the same as thatof the fourth embodiment. The Philips prism 213 herein has the structurein which two prisms of a triangular prism shape 213-1, 213-2 are bondedwith a spacer 213S in between to make a space between them as shown inFIG. 15 and in which a quadrangular prism 213-3 having the cross sectionof a trapezoid is bonded to the surface opposed to the bond surface ofthe prism 213-2 as shown in FIG. 14.

The operation of this optical block 20'will be described referring toFIG. 13. The description will be omitted as to the common parts to theother embodiments. Polarized light traveling in the X-direction isincident into this Philips prism 213 and only the B light thereof isreflected by the B light reflecting dichroic film formed on theX-directional end face of the prism 213-1. The B light reflected in thisway is again reflected in this prism 213-1 to enter the light valve 12Bfor B light. On the other hand, the R light and G light travels throughthe prism 213-2 and only the R light is reflected by the R lightreflecting dichroic film 213R formed at the border between the prisms213-2 and 213-3. The R light reflected is totally reflected at theinterface to the space formed by the spacer 213S (not illustrated inFIG. 13) to enter the light valve 12R for R light. The remaining G lighttravels straight through the prism 213-3 to enter the light valve 12Gfor G light. Beams emitted from the respective light valves 12R, 12G,12B travel in the reverse paths to be synthesized, and only modulatedlight is extracted by the PBS 17. The synthetic light is projectedthrough the projection lens 14 onto the screen not illustrated to form afull color image thereon.

FIG. 14 shows the direct mounting form of the light valves on thePhilips prism through the mounting members as in the first embodiment,but the light valve bodies may be attached to the Philips prism with anadhesive or the path length adjusting members may be interposed betweenthem.

The present embodiment also achieves the same effects as the fourthembodiment.

[Sixth Embodiment]

FIG. 16 is an overall schematic diagram of the sixth embodimentaccording to the present invention and FIG. 17 is a perspective view toshow the structure of the analyzing-synthesizing optical block 20thereof.

This embodiment is characterized in that the synthesizing optical systemis composed of two dichroic prisms 313-1, 313-2. Specifically, thedichroic prism 313-1 for synthesis of the R light and G light is bondedthrough path adjusting member 313S to the dichroic prism 313-2 forfurther combining this synthetic light with the B light. The dichroicprism 313-1 or 313-2 has the G light reflecting dichroic film 313G orthe B light reflecting dichroic film 313B, respectively, inside. Theother structure is basically similar to that of the second embodimentshown in FIGS. 5 and 6.

As apparent from FIGS. 16 and 17, the optical path lengths of therespective color beams are adjusted so as to be nearly equal by use ofthe path length adjusting members 15B-1, 15B-2, 15B-3, 15G, 15R, and313S. By securing the dichroic prism 313-2 to the base, the relativepositional relation is assured between the other components and thedichroic prism 312-2 accordingly. Therefore, the effect of expansion orthe like of the base can be suppressed with change in temperature andthe registration deviation and focus deviation can be suppressed, as inthe embodiments described above. Further, the present embodiment has anadvantage that the adjustment of optical path of the analyzing opticalsystem is easier, because the trichromatic separation optical system canbe composed of only the B light reflecting dichroic mirror and G lightreflecting dichroic mirror, though not illustrated.

As described above in each of the embodiments of the present invention,the invention can provide the projection type display apparatus that canminimize the deviation of corresponding pixels among the colors and alsominimize the focus deviation with change in the ambient temperature, byemploying the integral form of the light valves, PBSs, and the dichroicprism for synthesis of colors. Particularly, the base does not alwayshave to be made of a material having a small thermal expansioncoefficient, so that the housing can be a cheap member having a largethermal expansion coefficient but being lightweight and strong, such asthe aluminum alloys or FRP, which is effective.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

What is claimed is:
 1. An analyzing-synthesizing optical system unit forprojection image display apparatus in which beams of the three primarycolors of R, G, and B are modulated by respective, dedicatedpolarization beam splitters and light valves, the modulated beams areextracted, and a synthesizing optical system synthesizes the modulatedbeams of the three colors to output synthetic light,wherein said lightvalves and said polarization beam splitters are fixed as integrated withsaid synthesizing optical system and wherein optical path lengths ofoptical paths of the respective color beams, each optical path beingestablished by said light valve, said polarization beam splitter, andsaid synthesizing optical system, are approximately equal to each other;and wherein each of said polarization beam splitters is fixed in aconstituent member to which said synthesizing optical system is alsofixed.
 2. The analyzing-synthesizing optical system unit according toclaim 1, wherein each of said polarization beam splitters is fixed bybeing joined directly or indirectly through another optical member, toan entrance surface of said synthesizing optical system for each colorbeam.
 3. The analyzing-synthesizing optical system unit according toclaim 1, wherein a half wave plate is interposed between at least one ofsaid polarization beam splitters and said synthesizing optical system.4. The analyzing-synthesizing optical system unit according to claim 1,wherein each said light valve is fixed to said polarization beamsplitter by use of a mounting member.
 5. The analyzing-synthesizingoptical system unit according to claim 1, wherein each said light valveis fixed by being bonded to said polarization beam splitter.
 6. Theanalyzing-synthesizing optical system unit according to claim 1, whereinsaid synthesizing optical system is a cross dichroic prism.
 7. Theanalyzing-synthesizing optical system unit according to claim 1, whereinsaid synthesizing optical system is a combination of three triangularprisms or a combination of two triangular prisms with one quadrangularprism with reflecting films for reflecting respective, predeterminedcolor components being formed on predetermined surfaces.
 8. An opticalsystem unit for projection image display apparatus in which incidentwhite light is polarized and separated by a polarization beam splitter,the polarized light is separated into beams of the three primary colorsof R, G, and B by a separating-synthesizing optical system, the beamsare modulated by respective, dedicated light valves, the modulated beamsare synthesized again by said separating-synthesizing optical system,and said polarization beam splitter extracts only the modulated beams tooutput synthetic light,wherein said light valves and said polarizationbeam splitter are fixed as integrated with said synthesizing opticalsystem and wherein optical path lengths of optical paths of therespective color beams, each optical path being established by saidlight valve and said separating-synthesizing optical system, areapproximately equal to each other, and wherein said polarization beamsplitter is fixed in a constituent member to which saidseparating-synthesizing optical system is also fixed.
 9. The opticalsystem unit according to claim 8, wherein said polarization beamsplitter is fixed by being joined directly or indirectly through anotheroptical member, to an entrance/exit surface of saidseparating-synthesizing optical system.
 10. The optical system unitaccording to claim 8, wherein each said light valve is fixed to saidseparating-synthesizing optical system by use of a mounting member. 11.The optical system unit according to claim 8, wherein each said lightvalve is fixed by being bonded to said separating-synthesizing opticalsystem.
 12. The optical system unit according to claim 8, wherein saidseparating-synthesizing optical system is a cross dichroic prism.